1. Field of the Invention
The present invention relates to a control device, a control circuit, a control method, and a recording medium with a control program recorded therein, and specifically relates to a control device, a control circuit, a control method, and a recording medium with a control program recorded therein, which are capable of performing feedback control to reach an optimum lock point using an input signal whose duty value is other than 50%.
2. Description of Related Art
In recent years, in the course of enhancing the speed, integration density and performance of embedded control, it has become common to request one processor to perform multitasking.
Also, concurrently, hardware technology for including a processor and many peripheral devices in one chip has made substantial progress.
In order to provide higher-performance, low-cost control, optimization of the balance between the software (firmware) portion and the hardware portion is becoming increasingly important.
The feedback control to reach an optimum lock point has been performed using a dither signal with a duty value of 50%, so it has been necessary to accurately detect a phase shift caused within the control target by performing synchronous processing of a dither signal and a monitor signal within a DSP (Digital Signal Processor).
Accordingly, the current state is that the control circuits and the processors firmware have become complicated.
In view of this state, it is considered to be necessary to develop a control method for reducing the complexity of the control circuits and the processors firmware.
The technical documents filed for patent applications prior to the filing of the patent application for the present invention include documents each disclosing a semiconductor laser module capable of performing stable and high-accurate wavelength locking even when the temperature changes greatly (See, e.g., Japanese Patent Laid Open Publication No. 2003-264339).
They also include documents each disclosing a technology capable of precisely detecting a shift of the wavelength of light from a light source by disposing a first photo-detecting element, an etalon and a second photo-detecting element in this order and introducing light transmitted through the first photo-detecting element to the etalon (see, e.g., Japanese Patent Laid Open Publication No. 2003-69142).
Furthermore, they include documents each disclosing a technology that controls the temperature of an etalon element with high accuracy to avoid any influence from external temperature changes (see, e.g., Japanese Patent Laid Open Publication No. 2004-153176).
Furthermore, they include documents disclosing a technology for reliably finding a saddle point by: providing a path connecting two given local minimum points; and providing the present point, i.e., an attention point on the path to judge whether or not the attention point is on the boundary; if it is on the boundary, creating that point as a boundary point, thereby creating a boundary point; searching for a local minimum point of the intended function on the boundary composed by the created points; and when the local minimum point is found, outputting that point as a saddle point (see, e.g., Japanese Patent Laid Open Publication No. 2005-31888).
However, Japanese Patent Laid Open Publication Nos. 2003-264339, 2003-69142, 2004-153176, and 2005-31888 mentioned above include no descriptions or suggestions of necessity of performing feedback control so that a signal-wavelength input to a control target object becomes a specific signal-wavelength, using an input signal whose duty value is other than 50%.